Cylinder head for an internal combustion engine

ABSTRACT

A cylinder head for an internal combustion engine comprising a prechamber (3), wherein a prechamber gas valve (5) is fitted into a cavity in the cylinder head (2) and the prechamber gas valve (5) is connected to the prechamber (3) by way of a flow transfer passage (10), wherein the flow transfer passage (10) has a first portion (8) adjoining the prechamber gas valve (5) and a second portion (1) into which the first portion (8) opens, wherein the second portion (1) extends at least around a part of a periphery of the prechamber (3), wherein the second portion (1) has an uninterrupted peripheral surface apart from that opening (7) with which it passes into the prechamber (3).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage entry from, and claims benefit of,PCT Application No. PCT/AT2018/060315, filed on Dec. 21, 2018; entitled“CYLINDER HEAD FOR AN INTERNAL COMBUSTION ENGINE”, which is hereinincorporated by reference in its entirety.

BACKGROUND

The present invention concerns a cylinder head and an internalcombustion engine having such a cylinder head.

As from a certain diameter of the cylinder bore (about 150 mm), (gas)internal combustion engines are equipped with a prechamber for ignitionboosting. An ignition source—usually an ignition spark plug—whichprojects into the prechamber ignites the mixture which is presenttherein and which in the case of a flashed prechamber is relativelyrich, whereby ignition flares pass from the prechamber into a maincombustion chamber and ignite the mixture there.

There are various concepts in regard to the supply of fuel to theprechamber. In the case of an unflashed prechamber mixture is urged fromthe main combustion chamber into the prechamber in the compressionstroke. In the case of flashed prechambers there is moreover thepossibility of additionally supplying the prechamber with fuel. The fuelwhich is fed to the prechamber in case of a flashed prechamber cancorrespond to that in the main combustion chamber or can be differenttherefrom (in regard to its chemical composition and/or in regard to itsair excess number). That separate fuel supply is effected by way of aprechamber gas valve which can be arranged in the cylinder head directlyor indirectly (by way of a spark plug sleeve). Hereinafter, that fuelwhich is fed to the prechamber by way of the prechamber gas valve isreferred to as propellant gas.

A cylinder head of the general kind set forth is shown for example in EP3 064 755 A1. That specification discloses a cylinder head having acavity for receiving a prechamber gas valve arranged in the cylinderhead indirectly by way of a spark plug sleeve. The prechamber gas valveis connected to a prechamber by way of an inclinedly arranged flowtransfer passage, wherein in operation of the internal combustion enginepropellant gas is fed to the prechamber by way of that flow transferpassage. A similar concept of a flow transfer passage is known from EP 3061 939 A1.

EP 3 012 444 A1 discloses a configuration of a flow transfer passagewhich is implemented by a horizontal and a vertical bore for supplyingthe prechamber with a propellant gas coming from the prechamber gasvalve.

In addition, it is known from EP 3 012 431 A1 to provide a ring passageconnected to the prechamber gas valve by way of a flow transfer passage.The ring passage extends around the prechamber and is connected to theprechamber by a plurality of bores spaced radially from each other. Theplurality of bores provides that the propellant gas (coming from theprechamber gas valve by way of the flow transfer passage) is introducedas uniformly as possible into the prechamber and is there distributedwith a concentration which is as uniform as possible.

In a combustion cycle of the internal combustion chamber, propellant gasis fed to the prechamber by way of the flow transfer passage by theprechamber gas valve, thereby resulting in the prechamber in apropellant gas-air mixture (more precisely that propellant gas-airmixture is mixed in the prechamber with a fuel-air mixture which passesinto the prechamber from the main combustion chamber during thecompression stroke). Then, in the main combustion chamber, the fuel-airmixture supplied thereto is compressed in a compression stroke untilignition is triggered in the prechamber by a spark plug projectingthereinto. The propellant gas-air mixture ignited in the prechamberforms ignition flares which pass from the prechamber into the maincombustion chamber and initiate combustion in the main combustionchamber.

In general, the endeavor is to arrange the prechamber gas valve asclosely as possible to the prechamber as the propellant gas in the flowtransfer passage is not burnt or is only inadequately burnt duringcombustion. That partial or inadequate combustion of the propellant gasin the flow transfer passage leads to an unwanted increase in theemissions, in particular the HC emissions. The amount of propellant gaswhich is unburnt or insufficiently burnt in the flow transfer passagecan be reduced by reducing the length of the flow transfer passage andconsequently moving the prechamber gas valve closer to the prechamber.

By virtue of ignition in the prechamber and combustion of the propellantgas-air mixture in the prechamber the propellant-air mixture which ispresent in the flow transfer passage is also ignited, which can resultin the formation of combustion residues. Combustion residues in the formof deposits at the peripheral surface of the flow transfer passageand/or the prechamber gas valve have a very negative effect as justminor deposits in the flow transfer passage by virtue of its smallcross-section at the prechamber gas valve are sufficient to partially oreven completely block the passage.

BRIEF DESCRIPTION

The object of the invention is to provide a cylinder head which isimproved over the state of the art as well as an internal combustionengine having such a cylinder head.

That object is achieved by a cylinder head having the features of claim1 and an internal combustion engine having such a cylinder head.

In a cylinder head according to the invention, a prechamber gas valve isfitted into a cavity in the cylinder head, wherein the prechamber gasvalve is connected to the prechamber by way of a flow transfer passagewhich has a first portion adjoining the prechamber gas valve and asecond portion into which the first portion opens, wherein the secondportion extends at least around a part of a periphery of the prechamber,wherein the second portion has an uninterrupted circumference surfaceapart from that opening with which it passes into the prechamber.

This provides that the flow transfer passage is of such a length and isof such a cross-sectional area at least in a first portion adjoining theprechamber gas valve that in operation of the cylinder head mounted inan internal combustion engine in a compression stroke of the combustionprocess propellant gas which flew out of the prechamber gas valve formsa gas cushion in the flow transfer passage at least in the firstportion.

That propellant gas cushion does not have any oxygen component as thepropellant gas has not yet mixed with air. Due to the absence of anoxygen component in the propellant gas cushion, it does not take part inthe reaction (combustion) and thus no products of incomplete combustion(HC emissions) can be formed by the propellant gas cushion.

The provision of a flow transfer passage of such a length and such across-sectional area that the issuing propellant gas forms a gas cushionin the flow transfer passage, ensures at least in the first portion ofthe flow transfer passage that combustion residues do not settle in theform of deposits at the peripheral surface or the formation of suchdeposits is at least reduced. Possible deposits which nonetheless areformed at the peripheral surface of the flow transfer passage can beentrained by the through flow in the flow transfer passage by virtue ofa subsequent expansion phase in the combustion cycle (in which thehighest speeds in the through flow in the flow transfer passage occur,at least in the second portion of the flow transfer passage), and thusthe flow transfer passage can be cleaned.

In addition, combustion within the flow transfer passage is prevented bythe gas cushion consisting of propellant gas as the gas cushioncomprises almost pure propellant gas and cannot be ignited due to theabsence of oxygen. The gas cushion formed in that way from propellantgas forms so-to-speak a combustion barrier in the flow transfer passage.In other words the geometrical configuration of the flow transferpassage uses the propellant gas which is already present to prevent thecreation of deposits in the flow transfer passage near the prechambergas valve by not allowing combustion.

Advantageous embodiments of the invention are defined in the dependentclaims.

Particularly preferably it can be provided that the second portionextends in an angular range of about 20° to about 270°, preferably in anangular range of about 60° to about 180° around the prechamber.Accordingly it is possible to provide a prolongation of the flowtransfer passage in a particularly compact and space-saving fashion. Inthat case the flow transfer passage can extend in a circular path aroundthe prechamber or approach the prechamber in a spiral shape. Dependingon the respective demands involved, the flow transfer passage can openinto the prechamber radially, tangentially or along a secant, in whichcase it is possible to closed-loop/open-loop control or influence theflow into and the flow through the prechamber.

It can further be provided that a spark plug is provided as the ignitionsource in the cylinder head. In that case, commercially usual sparkplugs can be used. To accommodate the spark plug in the cylinder head,there can be provided a spark plug sleeve in the cylinder head.

It can be provided that the second portion extends in a plane parallelto a separation plane between the prechamber and the rest of thecylinder head, preferably between the prechamber and a spark plugsleeve. Such a provision of the second portion of the flow transferpassage provides a particularly simple and resource-sparing option forthe production of the second passage. Thus, at least the second portioncan be formed by at least one preferably milled groove in a wall of theprechamber and/or the rest of the cylinder head. In the assembled statein that case, the flow transfer passage is formed by the groove in awall of the prechamber and/or the rest of the cylinder head and a walladjoining that groove.

Consequently, it can be provided that the flow transfer passage isformed both by a wall of the prechamber and also by material of the restof the cylinder head.

It is preferably provided that a cross-sectional area of the flowtransfer passage, preferably at least over the length of the firstportion, is between about 1·π mm² and about 2.5²·π mm². It can, however,also be provided that the flow transfer passage is of a cross-sectionwhich varies over its length. Thus for example in certain regions of theflow transfer passage there can be provided a cross-section narrowing toachieve a throttle effect. Or it is possible for example to provide across-sectional enlargement (or also a space) in certain regions of theflow transfer passage to form a collecting location (for example for agas cushion). The flow speed of the propellant gas can be specificallyclosed-loop/open-loop controlled by a progressive narrowing orenlargement of the flow transfer passage.

In an embodiment, it can be provided that a total length of the flowtransfer passage is between about 30 mm and about 70 mm. However, thelength of the flow transfer passage can be selected in dependence on thesize of an internal combustion engine, the size of a combustion chamber,or the size of the cylinder head.

It can be provided that the flow transfer passage with respect to thecross-sectional area immediately downstream of the prechamber gas valveis of a (volumetric) equivalent length of about 15 to about 23 mm,preferably an equivalent length of about 16 to about 20 mm. In thatrespect, the equivalent length is calculated from a volume of the flowtransfer passage, that is required to form a sufficient gas cushionbefore the prechamber gas valve during combustion. That equivalentlength is thus to be interpreted as a measurement in respect of asubstitute volume. The equivalent length is not necessarily an actuallyimplemented structural size, but specifies a length which is to beprovided if the flow transfer passage were to be constructed with aconstant cross-sectional area, which cross-sectional area wouldcorrespond to the cross-section area immediately downstream of theprechamber gas valve (that gives the substitute volume—equivalent lengthmultiplied by the cross-sectional area immediately downstream of theprechamber gas valve). The actually structurally provided length of thetransfer flow passage results from that substitute volume (equivalentlength multiplied by the cross-sectional area immediately downstream ofthe prechamber gas valve) and the cross-sectional variation along theflow transfer passage.

In other words the equivalent length is the length of a notional passagewhich is of the same volume as the actual flow transfer passage, butthroughout is of that cross-sectional area of the flow transfer passage,that is immediately downstream of the prechamber gas valve.

It can preferably be provided that the flow transfer passage, preferablythe first portion, has a portion inclined substantially relative to aseparation plane between the prechamber and the rest of the cylinderhead. In that case, for example, it can be provided that the angle ofthe flow transfer passage, preferably of first portion, is 20° to 70°with the axis of symmetry of the prechamber gas valve. Such an inclinedconfiguration (at least of the first portion) of the flow transferpassage makes it possible to achieve particularly high mechanicalstability for the cylinder head. The fluidic flow configuration of thesupplied propellant gas is optimized by virtue of the fact that it doesnot have to flow through any acute angles. For the production of such agas passage, it can be provided that a flank of the cylinder head isarranged inclinedly. That, for example, can be so selected that theinclined flank is at a right angle to the axis of the flow transferpassage. That facilitates production of the flow transfer passage byboring. Particularly preferably it can be provided that the angle of theflow transfer passage relative to the axis of symmetry of the valve bodyis 20° to 30°.

It can be provided that a space is provided between a seat of the valvehead of the prechamber gas valve and a mouth opening of the prechambergas valve into the flow transfer passage. That is the case if the valvehead of the prechamber gas valve does not directly adjoin the prechamberor the flow transfer passage leading to the prechamber, but a hollowspace is formed therebetween. The provision of that space provides for aparticularly good flow of the propellant gas out of the prechamber gasvalve into the flow transfer passage.

It can preferably be provided that the space is of a very substantiallypear-shaped configuration, which tapers towards the prechamber. In thatway, the flow of propellant gas out of the prechamber gas valve into theflow transfer passage can be desirably influenced and nonetheless thevolume can be kept small.

Protection is further claimed for an internal combustion engine, inparticular a stationary internal combustion engine, having at least onecylinder head according to the invention.

The invention can preferably be used in a stationary internal combustionengine or for marine applications or for mobile applications likeso-called “non-road mobile machinery” (NRMM)—preferably each in the formof a reciprocating piston engine (preferably a gas engine). The internalcombustion engine can serve as a mechanical drive for example fordriving compressor installations or can be coupled to a generator toform a genset for generating electrical power.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are described with reference to thedrawings in which:

FIG. 1 shows a first embodiment of a cylinder head,

FIG. 2 shows the cross-section indicated in FIG. 1,

FIG. 3 shows a second embodiment of a cylinder head,

FIG. 4 shows the cross-section indicated in FIG. 3,

FIG. 5 shows an alternative embodiment to FIG. 4, and

FIG. 6 shows a further alternative embodiment to FIG. 4.

DETAILED DESCRIPTION

FIGS. 1 and 2 show a first embodiment of a cylinder head 2 for aninternal combustion engine having a prechamber 3. The prechamber gasvalve 5 and a spark plug (not shown for reasons of clarity) are fittedin a spark plug sleeve 4. In the installation position, the spark plugsleeve 4 is fitted into the cylinder head 2 of the internal combustionengine (not shown here in its entirety).

FIG. 1 shows a longitudinal section through the cavity of the cylinderhead 2 into which the spark plug sleeve 4 is fitted. The spark plugsleeve 4 includes a shaft which is concentric around the axis ofsymmetry S1 and comprises cylindrical portions for receiving a sparkplug and it has a bore with the axis of symmetry S2 for receiving aprechamber gas valve 5.

A flow transfer passage 10 leads from the prechamber gas valve 5 to theprechamber 3. The prechamber 3 comprises the actual prechamber space 6,that is to say a hollow space in which the ignition of mixture takesplace and the flow transfer bores 9, through which the prechamber space6 is connected to the main combustion chamber (not shown). Afterignition in the prechamber space 6, the ignition flares pass into themain combustion chamber by way of the flow transfer bores 9. In thepresent embodiment, the prechamber 3 is in the form of a componentseparate from the spark plug sleeve 4 and is connected, for examplepressed, to the spark plug sleeve 4.

The spark plug 6 (not shown for the sake of clarity) is screwed into thespark plug sleeve 4 by way of the spark plug bore 12, which isconcentric with the axis of symmetry S1, in such a way that itpreferably terminates flush with the prechamber 3 and its electrode orelectrodes project into the prechamber 3. The prechamber 3 is enrichedwith propellant gas by the prechamber gas valve 5 by way of the flowtransfer passage 10.

It can be clearly seen here how the flow transfer passage 10 issubdivided into a first portion 8 and a second portion 1. The firstportion 8 leads from a space 11, which is arranged at the prechamber gasvalve 5 and has a closed peripheral surface to the second portion 1 intowhich the first portion 8 transitions. The first portion 8 in that caseis in the form of a bore in the spark plug sleeve 4, which is inclinedat an angle β relative to the axis of symmetry S2 or also the axis ofsymmetry of the valve body.

FIG. 2 shows the section A-A indicated in FIG. 1 through the separationplane between the prechamber 3 and the spark plug sleeve 4. That sectionmakes it possible to see the second portion 1 of the flow transferpassage 10, which extends in an angular range a about a part of theperiphery of the prechamber 3, wherein the second portion 1 (apart fromthat opening 7 with which it opens into the prechamber space 6) has anuninterrupted peripheral surface. For the sake of clarity, the cylinderhead 2 is not shown in this Figure. In this embodiment, the secondportion 1 of the flow transfer passage 10 is provided by a milled groovein the spark plug sleeve 4, which is closed by the adjoining wall of theprechamber 3 and forms a passage (second portion 1 of the flow transferpassage 10).

FIGS. 3 and 4 show a second embodiment of a cylinder head 2 for aninternal combustion engine. Unlike FIGS. 1 and 2, in the embodiment ofFIGS. 3 and 4 the second portion 1 of the flow transfer passage 10 isprovided in the prechamber 3. That is particularly clear from FIG. 3.FIG. 4 in turn shows the section B-B indicated in FIG. 3 through theseparation plane between the prechamber 3 and the spark plug sleeve 4.

In FIGS. 3 and 4, the second portion 1 of the flow transfer passage 10extends in an angular range a around a part of a periphery of theprechamber 3, wherein the second portion 1 (apart from that opening 7with which it opens into the prechamber space 6) has an uninterruptedperipheral surface. In this embodiment, the second portion 1 of the flowtransfer passage 10 is provided by a milled groove in the prechamber 3,that is closed by the adjoining wall of the spark plug sleeve 4 andforms a passage (second portion 1 of the flow transfer passage 10).

FIGS. 5 and 6 show alternative embodiments of the second portion 1 ofthe flow transfer passage 10 in the same cross-section B-B as also shownby FIG. 4, that cross-section being defined by FIG. 3. These embodimentshowever can also be designed analogously in relation to the solutionshown in FIG. 1.

FIG. 5 shows an embodiment in which the second portion 1 of the flowtransfer passage 10 opens tangentially into the periphery of theprechamber space 6 with the opening 7. By virtue of the variation in theentry angle of the flow transfer passage 10, more precisely its secondportion 1, into the prechamber space 6, it is possible toclosed-loop/open-loop control flooding of the prechamber 3 by thepropellant gas. The second portion 1 of the flow transfer passage 10 isformed by a milled groove in the prechamber 3.

The embodiment shown in FIG. 6 has a second portion 1 of the flowtransfer passage 10, that has a cross-sectional narrowing 13 before theopening 7 into the prechamber space 6. By virtue of the variation in thecross-section of the flow transfer passage 10, more precisely its secondportion 1, upstream of the prechamber space 6, it is possible toclosed-loop/open-loop control the speed at which the propellant gasflows in. The second portion 1 of the flow transfer passage 10 is againprovided by a milled groove in the prechamber 3.

LIST OF REFERENCES

-   1 second portion-   2 cylinder head-   3 prechamber-   4 spark plug sleeve-   5 prechamber gas valve-   6 prechamber space-   7 opening-   8 first portion-   9 connecting passage-   10 flow transfer bores-   11 space-   12 spark plug bore-   13 cross-sectional narrowing-   S1 axis of symmetry-   S2 axis of symmetry-   α angular range-   β angle

1. A system, comprising: a cylinder head for an internal combustion engine comprising a prechamber, wherein a prechamber gas valve is fitted into a cavity in the cylinder head and the prechamber gas valve is connected to the prechamber by way of a flow transfer passage, wherein the flow transfer passage has a first portion adjoining the prechamber gas valve and a second portion into which the first portion opens, wherein the second portion extends at least around a part of a periphery of the prechamber, wherein the second portion has an uninterrupted peripheral surface apart from an opening between the second portion and the prechamber.
 2. The system of claim 1, wherein the cylinder head comprises a spark plug disposed in a spark plug sleeve.
 3. The system of claim 1, wherein the second portion extends in an angular range (α) of about 20° to about 270°.
 4. The system of claim 1, wherein a cross-sectional area of the flow transfer passage, at least over a length of the first portion, is between about 1·π mm² and about 2.5²·π mm².
 5. The system of claim 1, wherein a total length of the flow transfer passage is between about 30 mm and about 70 mm.
 6. The system of claim 1, wherein at least the second portion of the flow transfer passage is disposed between a first surface of the prechamber and a second surface of the cylinder head or a spark plug sleeve.
 7. The system of claim 6, wherein at least the second portion of the flow transfer passage comprises at least one groove in the first surface or the second surface.
 8. The system of claim 1, wherein the flow transfer passage with respect to a cross-sectional area immediately downstream of the prechamber gas valve is of an equivalent length of about 15 to about 23 mm.
 9. The system of claim 1, wherein the second portion of the flow transfer passage has a substantially parallel portion in relation to a separation plane between the prechamber and the cylinder head.
 10. The system of claim 1, wherein the first portion of the flow transfer passage has a portion inclined substantially relative to a separation plane between the prechamber and the cylinder head.
 11. The system of claim 1, wherein a space is provided between a seat of a valve head of the prechamber gas valve and a mouth opening of the prechamber gas valve into the flow transfer passage.
 12. The system of claim 1, wherein the flow transfer passage is of a cross-section varying over its length.
 13. The system of claim 1, comprising the internal combustion engine having the cylinder head.
 14. A method, comprising: forming at least a second portion of a flow transfer passage in a portion of a cylinder head of an internal combustion engine, wherein the flow transfer passage comprises a first portion coupled to the second portion between a prechamber gas valve and a prechamber space of a prechamber, wherein the second portion is disposed between the first portion and the prechamber space, wherein the second portion extends at least around a part of a periphery of the prechamber, wherein the second portion extends to an opening into the prechamber.
 15. The method of claim 14, wherein the portion of the cylinder head comprise a spark plug sleeve or the prechamber.
 16. The method of claim 14, wherein forming the second portion of the flow transfer passage comprises extending the second portion in an angular range (α) of about 20° to about 270°.
 17. A system, comprising: at least a portion of a cylinder head of an internal combustion engine, wherein the portion comprises at least a second portion of a flow transfer passage, wherein the flow transfer passage comprises a first portion coupled to the second portion between a prechamber gas valve and a prechamber space of a prechamber, wherein the second portion is disposed between the first portion and the prechamber space, wherein the second portion extends at least around a part of a periphery of the prechamber, wherein the second portion extends to an opening into the prechamber.
 18. The method of claim 17, wherein the portion of the cylinder head comprise a spark plug sleeve or the prechamber.
 19. The method of claim 17, wherein the second portion of the flow transfer passage extends in an angular range (α) of about 20° to about 270°.
 20. The method of claim 17, wherein the second portion of the flow transfer passage extends radially, tangentially, or along a secant into the prechamber via the opening. 